Data loggers log information over a desired period of time. Typically, they periodically sample input from a sensor, so that the sensor reading at each sampling may be stored and retrieved later together with the time of sampling. For example, to log temperature readings, a temperature sensor may be sampled and the temperature readings are stored.
There are many uses for data loggers, but one use of particular interest is to monitor temperature, for example in food storage or in a laboratory setting, to verify whether the temperature remained within desired ranges and, if not, to know how long the temperature remained outside the desired range. One such use is food storage. Another is to monitor the environment used for animal or plant husbandry. Yet another is for longer term laboratory experiments.
Data logs for temperature are particularly important for periods in which environmental control machinery is disrupted, for example, by a power outage. If a food freezer loses power, it is critical to have a log of temperature over the outage period that provides reliable information about the duration and level of temperatures within or exceeding a prescribed food storage temperature. In these situations, it is important that the logger have adequate back-up power to perform its function. Data loggers are described in U.S. Pat. No. 6,883,037, U.S. Pat. No. 6,826,664 and U.S. Pat. No. 5,623,416.